This invention relates generally to electrodes having surface bound electron-transfer catalysts.
The catalysts of the present invention are those which are used in mediating electron transfer processes. When attached to an electrode surface they act by altering the electromotive potential on the surface to which they are attached. When the molecule to be acted upon by the catalyst impinges upon the catalyzed surface, an electron transfer reaction occurs. The kinetics of this electron transfer process is affected by the positioning of the catalyst with respect to both the catalyzed surface and the reactive molecule.
An electron-transfer catalyst is generally a molecule which is capable of having overlapping electron spheres with both of the molecules to be acted upon. For example, in the case of electron-transfer from a molecule in solution to a conductive surface, the catalyst acts by having overlapping electron spheres with both the molecule in solution and the molecule making up the electronically conductive surface; by providing a continuous electron sphere overlap between the molecule in solution and the molecule making up the conductive surface, the electron-transfer catalyst increases the velocity of electron transfer between the molecule to be acted upon and the conductive surface.
Catalysts in general are usually employed in two forms. In one form the catalyst is immobilized on a support surface. Thus, the reactants to be catalyzed are caused to come in contact with the immobilized catalyst. For example, platinum can be absorbed on the surface of a carbon structure. Such a catalyst structure can be used for the production of hydrogen peroxide from hydrogen and oxygen by allowing the reactants, hydrogenn and oxygen, to flow past the platinum absorbed on the surface of the carbon.
A significant problem associated with utilizing an absorbed catalyst is that the catalyst can become deabsorbed. Such deabsorption, of course, presents many problems such as loss of the catalyst and/or contamination of the product.
Another approach to catalysis is to maintain the catalyst in a liquid carrier which includes the reactants. Such a procedure, of course, requires a separation step in order to prevent loss of the catalyst and also to remove the catalyst from the product. Obviously, such a procedure has disadvantages. Perhaps the most significant disadvantage, however, is associated with the requirement that the catalyst be separated from the reaction product. For example, the use of dichlorodicyanoquinone in the synthesis of ketones requires a laborsome separation of the catalyst from the ketone product.
As is well known in the art, electron-transfer catalysts are useful in a number of chemical and electrochemical processes. For example, in the generation of ketones from alcohols, discussed above, dichlorodicyanoquinone acts as an electron transfer catalyst.
Other examples of an electron transfer catalyst are the use of phthalocyanines, phenylporphyrins or dibenzotetraazaanulene organometallics in catalyzing the oxygen dissolution reaction in primary fuel cells.
Catalysts such as N,N'bisalkylated bipyridinium ions have been shown to catalyze the reduction of spinach ferrodoxin when adsorbed on gold while the gold electrode by itself will not catalyze this reaction. The adsorbed organic catalyst thus acts to reduce the over-potential of the electrode; but, the stability of this electrode is limited by the dissolution of the organic catalyst.
Electron-transfer catalysts suffer from a number of disadvantages, most of which are associated with the dissolution of the catalyst or separation of the catalyst from the reaction product.
An object of the invention is to immobilize an electron transfer catalysts on an electrode surface in a way that renders it resistant to loss or dispersion without significantly affecting its ability to function as a catalyst.